1. Technical Field
The present invention relates to a method for driving an electrophoretic display device, an electrophoretic display device, and an electronic device.
2. Related Art
There is known a type of an electrophoretic display device, in which an electrophoretic element, which includes electrophoretic particles and a dispersion medium, is interposed in a space defined between a pair of substrates. In this type of an electrophoretic display device, the mobility of the electrophoretic particles depends on temperature. Accordingly, the extensible application time of a driving voltage for the electrophoretic element is prolonged in a low-temperature environment (refer to, for example, JP-T-2007-501436) or an operation of repeatedly writing at every specific period is performed in order to ensure performance that stores and maintains a display (refer to, for example, JP-A-2007-187936 and JP-A-2007-187938).
According to approaches disclosed in JP-T-2007-501436 as well as JP-A-2007-187936 and JP-A-2007-187938, it is possible to compensate for a variation in the mobility of charged particles that is caused by a change in temperature. However, through studies conducted by the inventor et al., it was newly found that current balance is sometimes completely broken due to a great difference in the value of a current between white display and black display when the temperature of an application environment changes.
FIG. 9 is a graph showing the relationship between environment temperature and leak power. FIGS. 10A to 10C are graphs showing the results by measuring the values of the leak currents of white display and black display at environmental temperatures −5° C., 70° C., 110° C., respectively. The graph shown in FIG. 9 is produced by plotting the integrated values of the leak currents (i.e., leak powers) of the respective graphs in FIGS. 10A to 10C with respective to the respective environmental temperatures. As shown in FIG. 9, the difference between the leak power of white display and the leak power of black display increases with the rise in environmental temperature.
As such, if the current balance between white display and black display is broken, a large amount of current flows in a specific direction into an electrophoretic element or an electrode, so that the electrophoretic element or the electrode is vulnerable to degradation. In the examples shown in FIGS. 9 and 10A to 10C, a large amount of current flows from an Indium-Tin-Oxide (ITO) electrode, located over a display surface, toward an electrode over the opposite surface of an electrophoretic display device. In addition, degradation occurs due to reduction by the current. For example, impurity components are stuck to the ITO electrode, thereby coloring it. Such a problem may occur in the electrophoretic display device that has an electrode made of ITO or the like, which can be easily reduced. Furthermore, the problem may occur not only when the leak power of black display is relatively large but also when the leak power of white display is relatively large.